I would think the slight difference in speed is made up by the smaller draw and need for recharge of the battery.
You can get a smaller pulley but most I have seen are in the $25 range.
I have even read where someone took a saws all and cut the 7/16 pulley in half and added a flat washer between the two halves making it wider.
I just bought a 7/16" belt of the proper length and let it ride deep in the crank pulley. Been working great for several years that way.